I was brought up in an actively Liberal family, so I learnt the importance of by-elections. In my boyhood, a single Liberal by-election victory could add about 10 per cent to the party’s representation in the House of Commons. I remember when, in 1972, the party won Sutton and Cheam from the Tories with a 32 per cent swing. The victor was called Graham Tope. The headline in Liberal News, the party paper, was “Land of Tope and Glory”.

Even we laughed at this grandiloquence, but people like the now forgotten Mr Tope matter. Liberal Democrat recovery in modern times has worked from the local to the national. Sensing weakness in one of the two main parties locally, the Liberals have planted roots in an area, grasped the issues, won the council seats, pounded the pavements, and kept at it. Poor Mr Tope lost to the Conservatives two years later, but the party locally did not give up. Sutton and Cheam is a Lib Dem seat today.

So it was with Eastleigh on Thursday. The Liberal Democrats knew the place and the place knew them. They did not, in fact, do well – their vote fell even more than the Tories’ – but they were deeply enough entrenched to survive Chris Huhne’s lies and Lord Rennard’s allegedly wandering hands.

Once upon a time, the two big parties had this ability to plant themselves, even when the political soil was seemingly infertile. In the 1950 and 1951 elections, a young woman called Margaret Roberts was the Conservative candidate in Dartford. It was a Labour seat with a 20,000 majority, but by the time Miss Roberts had left to go and marry a Dartford businessman called Denis Thatcher, she had increased the membership of the constituency Conservative association to 3,160. I don’t suppose the safest Tory seat in the country has such a membership today. Certainly in the constituency in Sussex where we live, almost the truest-blue in the country, the association has, after its recent anti-gay-marriage resignations, only 666 members left. The story of Labour decline is not dissimilar.

This is a disaster. The end of a huge voluntary party run with military exactness means that campaigning now resembles dropping behind enemy lines. Brave canvassers from out of the area, however keen to win, cannot locate their position on the map or speak the lingo.

It is a terrible organisational problem, and votes, without organisation, trickle away. But it is worse: it is a profound cultural problem. The people who joined the future Mrs Thatcher’s Dartford association were not, for the most part, what would now be called political “wonks”. They were young, often hoping to marry one another. They tended to come from the aspiring lower middle class – secretaries in banks, local builders, family businesses. They disliked Labour because they saw it as the party of restrictions and trade unions. Much more important than whether they agreed with the Tories on actual policies was the fact that they regarded them as their natural home.

Out of this close identification between the party and hundreds of thousands of ordinary people with strong local ties grew – in a way that the Liberals’ extreme localism has never quite achieved – a mighty national presence. It was culturally, financially, morally, socially strong. That made it politically strong too. When Mrs Thatcher spoke about “our people”, she was doing two things at the same time – sticking up for her tribe and identifying the most dynamic force in the future of the nation.

Labour had its equivalent role in British life, which imploded with the trade union militancy and Left-wing infiltration of the Seventies. The Conservatives imploded later, after the political assassination of Mrs Thatcher.

Ever since, both main parties have become inauthentic. Rather than arising from powerful sections of the population, they seem to manipulate them. Unlike in, say, Italy, our political parties have kept the names which they had in the Cold War era, but they have become more volatile, Italian-style, than we think. They are like vehicles hijacked for a period by particular gangs of clever men (it is almost all men) and then driven until they crash.

The gay marriage smash-up among the Tories is an example of this effect. The rise of Ukip is proof of it. It is true that Ukip takes votes from all parties, but its roots are Tory. If the Conservative leadership had not gradually lost touch with its roots over a generation, Ukip would not exist. Labour’s negligence allowed the SDP to split it in the Eighties. Today, it is the Right which is busy dividing itself.

If you imagine Eastleigh as having been a general election, you will see that the result resembles the latest Italian effort – indecisive, and pretty bad for everyone except for the party which is not considered “serious” – in this case, Ukip.

David Cameron’s supporters hurry to point out that the result reflects badly on all the conventional parties and is not untypically extreme for mid-term by-elections. They are right. Nothing in the Eastleigh result says the Tories must lose next time. It even helps the Coalition function more calmly.

They are also right that Mr Cameron would be mad to alter his main policy course in response. The need is to build on his excellent party conference speech last autumn about enabling the people, especially the smaller businesses, who are fighting Britain’s “global race”. He is a much better leader than his main opponent or his Coalition partner. The more he can lead on the issues that count – the economy and public services in hard times – the better. I wish he would “kitchen-sink” our economic problems for the public, setting out their full extent and our prospects with sober honesty, and make sure that George Osborne does the same in the Budget. After all, Britain is borrowing £400,000 a minute: we all need explanation, rigour and hope.

But Eastleigh brings out something which more and more voters feel. A quarter of a century ago, when people used to complain in pubs that “they’re all the same”, I used to argue back: it seemed to me patently false. Today, I stay quiet. Nigel Farage says that we have three social democrat parties now. There is a bit of truth in that, but I would put it differently. It is not so much that they all think the same thing. It is more that they are all the same sort of people. They all belong to a political elite whose attitudes and careers are pretty different from those of the rest of us. The credit crunch has now lasted as long as the Second World War, but it has not seriously dented their way of life. This disconnect is made even more marked by the rising power of the EU – Nick Clegg is our first party leader to have started his politics in Brussels not Britain.

Such people, moving in their small world, lose touch with normal human instincts. How little they reacted, for example, when the European Court of Justice decreed this winter that equality rules should double the car insurance premiums paid by young women. And when the infinitely more terrible news of the 1,200 unnecessary deaths at Stafford Hospital was exposed in its full horror, no leaders of the Coalition saw at once (or at all) that such a failure of leadership demanded the immediate resignation of the chief executive of the National Health Service, Sir David Nicholson. That would just have been trouble, and establishments mind trouble more than anything else.

Well, now their very caution is bringing them trouble aplenty. An unworthy, Farage-ish bit of me says, “serves them right”.